Microprocessor having high current drive

ABSTRACT

An integrated circuit having a microprocessor core interfaced to large power transistors is described. This integrated circuit provides the capability to intelligently control and drive loads requiring currents exceeding 250 milli amps. The large power transistors are built in a technology compatible with the microprocessor core technology resulting in a more readily manufacturable circuit. The microprocessor core is layed out in a manner which provides the greatest distance between the most heat sensitive microprocessor core circuits and the power devices. On chip temperature sensing and feedback is provided for junction temperature monitoring and control.

FIELD OF THE INVENTION

This invention relates in general to the field of microprocessors andpower devices and more particularly, to a microprocessor having largecurrent drive capability, wherein integrated power devices exhibit a lowdrain-source on resistance (rdson) and are process compatible with themicroprocessor technology.

BACKGROUND OF THE INVENTION

Microprocessors, in the past, have been widely used to control andmonitor devices operating at voltage and power levels which exceed thecapabilities of the microprocessor itself. Typical examples includedriving fractional horsepower DC motors and solenoids in consumerelectronics, small industrial machines, automotive applications, roboticmechanical controls, etc. The use of the microprocessor as a controllingand monitoring device is extremely useful due to the flexibility andprocessing power of the microprocessor, and since often times thecontrolling input signals to the microprocessor are in digital formwhich are readily usable by the microprocessor. Further, the uniquecontrol program required to instruct the microprocessor may be stored inmask programmable Read Only Memory (ROM) or Electrically ProgrammableRead Only Memory (EPROM). Typically the outputs of the microprocessor,however, are limited to a voltage range equal to that of themicroprocessor power supply, and to current drive capabilities in therange of 12 to 48 milli-amps per output driver.

Further increases in output drive capability on the microprocessor ispossible by using bipolar transistors in the output circuits. Themajority of microprocessors currently being used are Complementary MetalOxide Semiconductor (CMOS) due to the high transistor densities andlower power consumption requirements. The bipolar devices, however,require a relatively large base drive current and additionally, severalmore masking steps in the manufacturing process. Also, bipolar devicesrequire a large amount of silicon real estate and dissipate largeamounts of power relative to several special purpose MOS power devicessuch as Lateral DMOS (LDMOS), Vertical DMOS (VDMOS), and Updrain DMOS(UDMOS). The high base drive current problem of the bipolar devices maybe reduced somewhat by using Darlington transistor pairs in their place,but the requirements of large silicon area still exists and additionallyundesirable forward voltage drops develop across the Darlingtontransistor pairs which make these devices unsuitable for manyapplications. If the bipolar output driver were driving 100 milli-ampsand the transistor fell into the linear region of operation from thesaturation mode, the bipolar device would rapidly heat and likelydestroy the microprocessor circuits. Integrated bipolar outputtransistors are therefor limited in their application due to cost andpower dissipation considerations.

It would be advantageous to provide a special purpose microprocessorcapable of providing high current output capabilities on chip. Thiscould provide cost savings as well as decrease the package size relativeto a microprocessor driving a separate power device. This provides theability to place a single controlling-driver chip in areas where it isnot currently feasible to place a multiplicity of chips due tointerconnect and mounting problems. The microprocessor also has theability to closely monitor the temperature of the power devices and takecorrective action to avoid damage caused by overheating. Adding powerdrivers to the microprocessor requires solving problems of hightemperatures, high power dissipation, collecting excessive substratecurrents, and providing higher voltages than provided by the powersupply. Additionally it is desirable to have a power device that isprocess compatible with an existing microprocessor technology in orderto utilize an existing microprocessor design.

Thus, what is needed is a microprocessor having large current drivecapability, wherein integrated power devices exhibit a low drain-sourceon resistance (rdson) and are process compatible with the microprocessortechnology.

SUMMARY OF THE INVENTION

Accordingly, it is an object of the present invention to provide animproved microprocessor having large current drive capability.

It is a further object of the present invention to provide amicroprocessor circuit having power devices exhibiting a low rdson.

It is yet a further object of the present invention to provide amicroprocessor having power drivers wherein the power driversincorporate a similar process technology as the microprocessor core.

In carrying out the above and other objects of the invention in oneform, there is provided an integrated circuit comprising amicroprocessor core having a power output driver wherein said poweroutput driver provides at least 250 milli-amps current drive and iscontrolled by the microprocessor core.

The above and other objects, features, and advantages of the presentinvention will be better understood from the following detaileddescription taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is a block diagram of a microprocessor core driving internalpower output devices.

FIG. 2 is a schematic diagram of a power output driver configured as anH switch.

FIG. 3 is a schematic diagram of a temperature sense circuit.

FIG. 4 is a block diagram of a cross sectional plan view of theintegrated circuit layout of the present invention.

FIG. 5 shows in cross sectional view a portion of an integrated circuitof the present invention including a power device and a microprocessorcore device.

DETAILED DESCRIPTION OF THE INVENTION

Many circuit and system advantages can be realized by integrating adedicated microprocessor core on the same substrate as that of largepower drivers and their associated control circuits. In larger systems,the main controlling microprocessor may be allowed to spend more time onother system functions since it will not be required to spend as muchCPU time instructing and monitoring the integrated microprocessor-powerdevice due to the processing capabilities of the microprocessor-powerdevice. Additionally, the integrated microprocessor-power device is ableto monitor the substrate temperature and hence the operating temperatureof the power driver portion of the integrated circuit directly sincethey share the same substrate. There are also the cost and speedadvantages of the reduced packaging requirements.

Referring to FIG. 1, a block diagram representation of amicroprocessor-power integrated circuit 10 is shown. A microprocessorcore 5 is connected to a V_(DD1) but 1 and a ground supply bus 2(V_(SS1)). An internal data bus 6 connects a portion of themicroprocessor core 5 to a control and driver circuit 7, a temperaturesense circuit 8, and to a power output driver 9. The microprocessor core5 is also connected to a plurality of input/output pads 11 for receivingcontrol instructions from an external source. The power output driver 9is connected to its own voltage supply busses V_(DD2) bus 4 and V_(SS2)bus 3, in order to minimize the effects of noise due to large currentspikes through the power output driver 9 on the microprocessor core 5voltage supply levels. The power output driver 9 is further connected tooutput terminals 13 and 14 for driving a load 15.

The microprocessor core 5 typically contains at least a minimum amountof processing and control circuity, including a Central Processing Unit(CPU), CPU control circuit, Arithmetic Logic Unit (ALU), internalcontrol registers, pointers, and program counters. This minimumconfiguration provides a microprocessor core with the ability tocontrol, monitor, and change control based on instruction and feedbacksignals. The microprocessor core 5, for example, receives its controland feedback signals from both the plurality of input/output pads 11 andthe internal data bus 6. The power and output driver 9 can receivedigital signals directly from the microprocessor core 5 and send backstatus information via the data bus 6. Significantly more processingpower is added to the microprocessor core 5 by the inclusion ofadditional circuits including Static Random Access Memory (SRAM), ROM,Analog to Digital Converters (ADC), and timers, etc.

The inclusion of SRAM and ROM allow the microprocessor core 5 to operatemore independently from outside control since a control program may bestored in ROM and intermediate data may be stored in SRAM. In thepresent invention, an ADC is used in the microprocessor core to convertan analog signal from the temperature sense circuit 8 to a digitalsignal which may be processed by the microprocessor core 5 CPU. Stillmore versatility can be added by the inclusion of EPROM which allows thecontrol program to be modified, or a new control program to be storedfor new applications. An example of a microprocessor core currentlyavailable for use as the intelligent circuit control portion of thepresent invention is the Motorola 68HC05 microprocessor core.

In operation, the microprocessor-power integrated circuit 10 receivesits external commands from the plurality of input/output pads 11. Atypical example would be a command to the microprocessor-powerintegrated circuit 10 to drive a DC motor (load 15) in the forwarddirection. The control program stored in ROM would then direct themicroprocessor core 5 to provide the correct sequence of signals to theinternal data bus 6 which are then received by the control and drivercircuit 7 and the power output driver 9. The control and driver circuit7 is connected to the power output driver 9 by a driver bus 16 and hastwo basic functions which include providing a driver voltage whosemagnitude can be greater than the magnitude of the voltage level of theV_(DD1) supply voltage, and providing the necessary current drive toturn the power output driver 9 on and off within a specified timeinterval. If the magnitude of the V_(DD1) supply voltage is greater thanthe magnitude of the V_(DD2) supply voltage, then the magnitude of thedriver voltage may be equal to the V_(DD1) supply voltage and stillachieve minimum rdson.

A typical method of providing a driver voltage having a magnitudegreater than that of the supply voltage as in the control and drivercircuit 7 is by the use of a charge pump. A charge pump is a circuitthat uses voltage multiplication techniques to make available a voltagewhich is greater than the voltage sourcing the charge pump and is wellunderstood by those skilled in the art. The charge pump voltage is usedto power the rest of the control and driver circuits 7. Because thepower output driver 9 is large, it is necessary to provide more drivethan is typically available from a microprocessor core input/output bus(I/O). Also the power output driver 9 requires an overdrive voltage tominimize its rdson (the channel resistance of a transistor in the onstate) when sinking and sourcing large currents. Hence the control anddriver circuit 7 provides buffers having the necessary drive capabilityto sufficiently drive the power output driver 9. Furthermore themagnitude of the driver voltage reaches a magnitude equal to themagnitude of the charge pump voltage in order to provide the necessaryoverdrive.

FIG. 2 depicts in schematic form the devices comprising the power outputdriver 9 as coupled to the load 15. Structures of FIG. 1 which are shownin FIG. 2 are identified by the numbers in FIG. 1. In a minimumconfiguration, a power output driver might comprise only a single powertransistor giving it the capability to sink or source a single largecurrent. The power output driver 9 shown in FIG. 2, however, utilizesfour power devices configured as an H switch giving it the additionalcapability of driving a DC motor in both a forward and reversedirection. A power transition 17 has a source connected to the V_(DD2)bus 3, a gate connected to a driver bus node 16', and a drain connectedto the output terminal 13. A power transistor 18 has a source connectedto the V_(DD2) bus 3, a gate connected to a driver bus node 16", and adrain connected to the output terminal 14. The load 15 is coupledbetween the output terminals 13 and 14. Power transistors 19 and 21 havetheir sources connected to the V_(SS2) bus 4, their gates connected tothe driver bus nodes 16" and 16', respectively, and their drainsconnected to the output terminals 13 and 14, respectively. There areseveral types of power transistors which are suitable for use as thepower transistors 17, 18, 19, and 21, including but not limited tolateral, vertical, and updrain DMOS transistors.

The power transistors 17, 18, 19, and 21 are manufacturable in a processwhich is similar to that of the microprocessor core 5, are efficient insilicon area required for layout, and have minimum power dissipationtherein minimizing junction temperatures. N-type, lateral DMOS powertransistors which have the aforementioned characteristics are used inthe preferred embodiment of the present invention. As mentionedpreviously, the driver voltage controlling the power output drivercircuit 9 has a magnitude greater than the supply voltage V_(DD2). Theneed for this is because the power transistors 17 and 18 are N-type andtheir gates must therefor be driven to a potential that is at least athreshold voltage above the potential of their sources (V_(DD2)) inorder to operate in the saturation region and thus minimize rdson.

If the load 15 is a DC motor, applying a high driver voltage at thegates of power transistors 17 and 21 will cause current to flow throughthe load in a forward direction (from output 13 to output 14) which willcause the DC motor to rotate in a forward direction. By applying a highdriver voltage to the gates of power transistors 19 and 21 a reversecurrent flows through the DC motor (from output 14 to output 13) whichcauses the DC motor to rotate in a reverse direction. The currentrequirements of a fractional horsepower DC motor can easily exceed 0.25amps which requires the power transistors 17, 18, 19, and 21 to have avery low rdson (typically below 1 ohm). A low rdson not only providesoptimal motor operation, but also keeps the power dissipation in thepower output driver 9 to a minimum which is necessary to limit thesubstrate temperature on which the microprocessor core 5 resides. Sincethe microprocessor core 5 controls the control and driver circuit 7 andhence the driver voltage, the driver voltage can be pulse widthmodulated to control the speed of the DC motor (load 15) or the amountof current flowing through the power output driver 9. This is especiallyuseful since temperature information can be fed back to themicroprocessor core 5 via the temperature sense circuit 8, and themicroprocessor core 5 can then reduce the current flow through the poweroutput driver 9 if the junction temperature exceeds a predeterminedvalue.

An example of a circuit capable of sensing junction temperatures on asubstrate is illustrated in FIG. 3. A current mirror 22 is formed byfield effect transistors 23 and 24 wherein their sources are connectedto the V_(DD1) bus 1, and their gates are connected to the drain of thefield effect transistor 23. A diode 25 has an anode connected to thedrain of the field effect transistor 23 and a cathode coupled to theV_(SS1) bus 2 via a resistor 26. The drain of the field effecttransistor 24 is coupled to the V_(SS1) bus 2 via a resistor 27. Thediode 25 is a temperature sensing diode in that it is located in theproximity of the power output driver 9 and its linear temperaturecoefficient is used to track changes in temperature. As the junctiontemperatures of the microprocessor-power integrated circuit 10 increasedue to the current flowing in power output driver 9, the temperature ofthe diode 25 will change proportionately. It is well known that aforward biased PN junction has a forward voltage drop which varies by 2milli Volt/C up to 125C, given a constant current source (provided bythe current mirror 22). As the temperature increases then, an increasingvoltage differential is created between the drains of the field effecttransistors 23 and 24.

The cathode of the diode 25 is connected to the noninverting input of anamplifier 31, and the drain of the field effect transistor 24 isconnected to the inverting input of the amplifier 31 by a resistor 28.The output of the amplifier 31 is connected to a node 32 and furtherconnected to the inverting input via a resistor 29. The difference involtage between the noninverting and inverting inputs of the amplifier31 is amplified with the amount of amplification determined by the ratioof the resistors 28 and 29. The node 32 is connected to themicroprocessor core 5 via the data bus 6. If the temperature of thediode reaches a predetermined point, then the magnitude of the output atthe node 32 will be an indication to the microprocessor core 5 to takecorrective action. The corrective action from the microprocessor core 5can be preprogrammed in ROM and may vary from a warming message, toreducing or shutting off the driver voltage to the power output driver9.

Because of the large currents flowing through the power output driver 9,it is advantageous to physically locate the microprocessor core 5 at athe maximum distance from the power output driver 9. This is a result ofboth junction temperature and excessive parasitic substrate currents.FIG. 4 shows a floorplan of the microprocessor-power integrated circuit10 wherein the major circuit blocks are shown as they are locatedrelative to each other. The numbers used to identify structures in FIG.1 are used in FIG. 4 to identify the same structures. The microprocessorcore 5 is layed out in a manner that places the memory circuits at amaximum distance from the power output driver 9. The memory circuits,and especially the SRAM is particularly sensitive to thigh temperatureand high substrate currents. This further allows the microprocessor core5 to be arranged in the most suitable position. In other words havingthe least heat sensitive circuits of the microprocessor core 5 towardsthe power output driver 9 and the more heat sensitive circuits near thememory blocks. Least heat sensitive circuits include the I/O bus, whilemore heat sensitive circuits vary depending on the configuration of themicroprocessor core.

The control and driver circuit 7 is located between the microprocessorcore 5 and the power output driver 9 further buffering the two circuits.This is also the logical placement since the control and driver circuitreceives its signals from the microprocessor core 5 and then drives thepower output driver 9. The diode 25 of the temperature sense circuit 8is located next to the power output driver 9. A deep guard ring 34 isshown surrounding the power output driver 9 which acts to collect thesubstrate currents. The deep guard ring 34 is connected to the V_(SS2)bus 3 and is made up of a p+region diffused into a p-well (thuscollecting substrate currents deeper in the substrate due to theincreased depth and area of the p-well). The deep guard ring 34 iseffective for collecting the potentially large parasitic substratecurrents because it extends farther down into the substrate 40 than justa p+ring. The deep guard ring 34 is an example of an effective isolationstructure and it should be obvious to one skilled in the art to usemodified structures as required in different technologies. Themicroprocessor core 5 is a predesigned standard cell block andrepresents a known processor to the industry. Cost and familiarityproblems would make designing from scratch a microprocessor core justfor this application very expensive. It is advantageous to thus mergethe technology of the power output driver 9 in a way that does notrequire redesign of the microprocessor core 5.

Transistor structures of both the microprocessor core 5 and the poweroutput driver 9 are shown in cross sectional view in FIG. 5 as devices35 and 36, respectively. The devices 35 are typical of devices found ina standard N-well CMOS process. The device 36 uses the same structuralelements as devices 35 with the addition of a PHV-well 42 (high voltageP-well) being formed in an N-well 38 and thus forming a portion of thepower output driver 9. It is possible then, to build the microprocessorcore 5 on the same substrate as the power output driver 9 by masking thedevices 35 during the implanting of the PHV-well 42 so that the PHV-well42 exists only in the device 36. Although an N-well process in a P-typesubstrate has been shown, it would be obvious to one skilled in the artthat the complementary structure of P-wells in an N-type substrate is aviable alternate structure.

In the devices 35, the first region formed is an N-well 37 which isdiffused into a substrate 40. Simultaneously, the N-well 38 in device 36is also diffused into the substrate 40, with the doping concentrationsof the N-wells 37 and 38 being equal and greater than the dopingconcentration of the substrate 40. The PHV-well 42 is then formed in theN-well 38 in the device 36 having a doping concentration which isgreater than that of the N-well 38. P-type regions 39 and 44 are thenformed in the N-well 37, and the PHV-well 42, respectively. N-typeregions 41, 43, and 45 are simultaneously formed in the substrate 40,the PHV-well 42, and the N-well 38, respectively. The dopingconcentrations of the N-type regions 41, 43, and 45, and the P-typeregions 39 and 44, are all greater than the doping concentration of thePHV-well 42. An oxide 46 is grown on the surface, and gates 47, 48, and49 are deposited in a manner well known to those skilled in the art.

The P-type regions 39 in combination with the gate 47 form a p-typefield effect transistor 51, and the N-type regions 41 in combinationwith the gate form a N-type field effect transistor 52. Thesecomplementary field effect transistors 51 and 52 then form the necessarybuilding blocks of the microprocessor core 5. A portion of the poweroutput driver 9 is depicted as an N-type LDMOS device wherein the P-typeregion 44 provides an ohmic contact to the PHV-well 42 in order to backbias the source of the device 36. The N-type region 43 forms a donutshaped region which surrounds the P-type region 44. Similarly, theN-type region 45 forms a donut shaped area which surrounds the PHV-well42. The gate 49 also forms a donut shaped between the N-type regions 43and 45.

The device 36 is repeated to form an array in which all devices are thencoupled in parallel to provide a power transistor. The guard ring 34 asshown in FIG. 4 surrounds the device 36 (or array of devices 36) and ismade up of a P-type region formed in a PHV-well. As the number ofdevices in the array increases, so does the channel width of the powertransistor. A low rdson is accompanied by the combination of the largechannel width as provided for by the number of devices as and theefficiency of the structure of the device 36. The channel region of thedevice 36 is formed by the area of the PHV-well 42 and the N-well 38under the gate 49. A current flows laterally along the surface (hencethe term LDMOS) from the N-type region 43 to the N-type region 45.Because the current flow is lateral and not vertical to the substrate,it is possible to include several power transistors as used in the poweroutput driver 9 on the same substrate. There are numerous variations ofthe device 36 which are suitable for this application.

By now it should be appreciated that there has been provided amicroprocessor having large current drive capability, wherein integratedpower devices exhibit a low drain-source on resistance (rdson) and areprocess compatible with the microprocessor technology.

We claim:
 1. An integrated circuit comprising:a microprocessor core; andat least one power output device coupled to said microprocessor core forproviding a current drive capability of greater than 0.25 amps.
 2. Theintegrated circuit according to claim 1 wherein said microprocessor coreand said at least one power output device are manufacturable in asubstantially similar CMOS process technology.
 3. The integrated circuitaccording to claim 1 wherein said at least one power output device hasan rdson which is less than 1 ohm.
 4. The integrated circuit accordingto claim 1 further comprising a first means coupled to saidmicroprocessor core and to said at least one power output device forproviding a driver voltage to said at least one power output device,wherein the magnitude of the driver voltage is greater than themagnitude of a first supply voltage supplied thereto.
 5. An integratedcircuit comprising:a first supply voltage bus for receiving a firstsupply voltage; a second supply voltage bus for receiving a secondsupply voltage; a third supply voltage bus for receiving the firstsupply voltage; a fourth supply voltage bus for receiving the secondsupply voltage; a microprocessor core coupled between said first andsecond supply voltage buses; a first means coupled between said firstand second supply voltage buses and to said microprocessor core forreceiving at least one control signal from said microprocessor core andproviding a driver voltage having a magnitude greater than the magnitudeof the first supply voltage; and at least one power output devicecoupled between said third and fourth supply voltage buses and coupledto said first means for receiving the driver voltage for driving a loadrequiring at least 0.25 amps.
 6. The monolithically integrated circuitaccording to claim 5 further comprising an isolation means coupled to avoltage and located between said at least one power output device andsaid microprocessor core for collecting substrate currents.